The present invention relates to a numerically controlled machine tool for machining a large workpiece such as an aircraft part mounted on a workpiece support unit by moving a spindle having a tool mounted thereon in the directions along an X-axis, a Y-axis and a Z-axis with respect to the workpiece.
In production of an airframe of an aircraft, a method has been conventionally employed in which component parts of the airframe are divided into a plurality of segments and the segments are machined and joined with each other with bolts and rivets. In recent years, however, the trend is toward integrating these parts as far as possible and thereby reducing the jointed portions. As a result, the parts to be machined have increased in size and have become complicated in shape, thereby giving rise to the demand for a novel machine tool for machining such parts.
The unique performance requirements of such a machine tool include the provision of a table on which a large workpiece can be mounted, the provision of a sufficient long stroke in feed axes to machine a large workpiece and the possibility of machining a large part having a complicated shape at any points and in any kind of shapes by a single setup. Further, such parts are required to be machined efficiently, at high speed and with high accuracy. Also, in view of fact that a desired size of a workpiece to be machined varies from one machine tool user to another, the machine tool of a size required by each user can preferably be produced and installed in the factory quickly and at an appropriate time.
For the purpose of fixedly mounting a large workpiece, the table of the machine tool must be large, and it is necessary to take into consideration that the movability of the large table in the directions along three orthogonal linear feed axes, i.e., an X-axis, a Y-axis and a Z-axis, or in the directions along three rotational feed axes, i.e., an A-axis, a B-axis and a C-axis, is disadvantageous from the viewpoint of ensuring the high-speed, high-accuracy machining. Therefore, a machine tool for machining a large part, unlike normal machine tools, is required to have a fixed table and also requires that the spindle rotating with the tool held thereon is provided with orthogonal linear feed units and rotational feed units and is thereby movable in the directions along orthogonal linear feed axes and in the directions along rotational feed axes.
In addition, since a large workpiece is liable to deteriorate an efficiency of a workpiece setup process, the table for fixedly mounting the workpiece thereon is required to include means for automatically changing the workpiece for improving an efficiency of the setup process and an operating rate of the machine tool.
It is noted that the X-axis and the Y-axis are orthogonal to each other in a vertical plane, and extend horizontally and vertically, respectively, while the Z-axis extends in a horizontal direction perpendicular to both the X-axis and the Y-axis. It is also noted that the directions along the A-axis, the B-axis and the C-axis are defined as the directions of rotation about the X-axis, the Y-axis and the Z-axis, respectively.
A first prior art available for satisfying these requirements is a symmetric multiaxial linear motor machine tool described in Japanese Unexamined Patent Publication (Kokai) No. 8-318445. The machine tool includes a vertical gantry movable in a direction along the X-axis on vertically opposed frames, a saddle movable in a direction along the Y-axis on the vertical gantry, a ram adapted to be movable in a direction along the Z-axis on the saddle, a spindle head disposed at the front end portion of the ram for rotatably supporting a spindle having a tool mounted thereon, and a table fixed on the front portion of the frame for mounting a workpiece thereon. The X-, Y- and Z-slides are driven in the feed directions along the X-, Y- and Z-axes by linear motors. The vertical gantry is guided on two sides, upper side and lower side, with respect to the frame and driven by the linear motors. The arrangement of a stator (static element) and a mover (moving element) of the linear motor is symmetrical on the upper and lower sides of the frame so that the attraction forces of the stators acting on the movers, in both the upper and lower linear motors, are vertically offset from each other.
A second available prior art is a machine tool described in Japanese Unexamined Patent Publication No. 9-262727. The machine tool includes a vertical bed in the shape of a rectangular frame having a through opening at the center thereof in front view, an X-slide in the shape of a rectangular frame movable in a direction along the X-axis on the front side of the vertical bed and having a through opening at its center in front view, a Y-slide adapted to be movable in a direction along the Y-axis while being supported and guided in the through opening of the X-slide, a Z-slide adapted to be movable in a direction along the Z-axis while being supported and guided by the Y-slide, a spindle head disposed at the front end portion of the Z-slide for rotatably supporting a spindle having a tool mounted thereon, and a table fixed on the front portion of the vertical bed for mounting a workpiece thereon. The X-, Y- and Z-slides are guided by a pair of rail-shaped guides and driven in the feed directions along the X-, Y- and Z-axes by a pair of linear motors.
Further, a third available prior art is a workpiece pallet exchange method described in Japanese Unexamined Patent Publication No. 60-29261. The machine tool with a pallet changer disclosed in this patent publication includes a machine body for machining a workpiece by relative movement in directions along the X-, Y- and Z-axes between a spindle head for rotatably supporting a spindle having a tool mounted thereon and a table for mounting the workpiece thereon, and a pallet changer disposed adjacent to the machine body for giving and receiving the pallets to/from the table to exchange them. The pallet changer has a plurality of surfaces for mounting pallets thereon and is so structured to rotate about a horizontal rotational axis and thereby to index a w pallet change position, a standby position or a workpiece cleaning position.
As described above, a large machine tool for machining a large part such as a machine tool for machining aircraft parts is generally provided with a fixed, immovable table for mounting a large workpiece thereon, and a rotating spindle thereof having a tool held thereon is provided with an orthogonal linear feed units and/or rotational feed units, thereby allowing for the movement of the spindle in the directions along the X-, Y- and Z-axes and the rotation thereof in the directions along the A-, B- and C-axes. In addition, such machine tool generally has a horizontal spindle, which can move in a relatively long stroke along the X- and Y-axes. Therefore, a tall, large column is moved by being guided on the bed in the horizontal direction along the X-axis while the spindle head moves on the column in the direction along the Y-axis.
As described above, the larger workpiece results in an increased time for the setup process including operations of mounting the workpiece on the table and removing chips from the workpiece or demounting the workpiece from the table after machining. Therefore, during the setup process, the operation of the machine tool is inevitably stopped, thereby resulting in the problem of a low machine operating rate. Further, a movable body (for example, the spindle head and the column) moved in the direction along the X-axis is unavoidably larger and heavier. This makes it difficult to feed the movable body at high speed and also causes another problem of making it difficult to maintain a high positional accuracy in direction along the X-axis due to friction resistance caused by the weight of the movable body moved in the direction along the X-axis.
A method for solving the problem of the reduced working efficiency and the low machine operating rate due to the longer time consumed for the setup process is to add a pallet changer, as described in Japanese Unexamined Patent Publication No. 60-29261, to the machine tool. In view of the need to handle a large workpiece, however, such machine tool requires a larger installation space and a larger-scale structure which in turn causes another problem of a considerably high cost.
On the other hand, a method conceivable for solving the problem of the larger, heavier movable body of the spindle support structure is to use a machine tool described in Japanese Unexamined Patent Publication No. 8-318445 or No. 9-262727 described above, in which a base is constituted of a frame structure having upper and lower X-axis guides for guiding an X-axis slide of a similar frame structure at two upper and lower X-axis guides. Guiding and driving the movable body at upper and lower sides as described above can avoid a cantilevered state of the movable body, thereby making it possible to ensure a movable body having a relatively lighter weight but a required rigidity. Further, a high-speed feed can be achieved by using linear motors as a means for driving the movable body.
However, a new particular problem is caused by a machine tool requiring a longer stroke in a direction along the X-axis than a standard machine tool. More specifically, the longer length of stroke along the X-axis can require a longer movable cover of a telescopic type or a take-up type covering the feed mechanism and the guide along the X-axis for protection from the chips produced from the workpiece by machining process, and this longer movable cover often develops a malfunction. This problem is indicated in neither Japanese Unexamined Patent Publication No. 8-318445 nor No. 9-262727 which is not intended for a machine tool having a relatively longer stroke in the direction along the X-axis. Also, in spite of the lighter X-axis slider, the longer stroke in the direction along the Y-axis imposes some degree of load on the X-axis guide, thereby giving rise to the need of ensuring a safety factor over the service life thereof.
The present invention has been developed in view of these problems, and the object thereof is to provide a numerically controlled machine tool capable of machining a large workpiece at high speed with high accuracy and of facilitating the setup process for a large workpiece. Another object of the present invention is to provide a numerically controlled machine tool for machining a large workpiece with a high machine operating rate. Still another object of the present invention is to provide a numerically controlled machine tool having a long stroke along the X-axis which can be easily manufactured and installed. Yet another object of the present invention is to provide a numerically controlled machine tool for machining a large workpiece in which chips can be easily disposed of.
According to a first aspect of the present invention, there is provided a numerically controlled machine tool for machining a workpiece mounted on a workpiece support unit by moving a spindle having a tool mounted thereon in directions along an X-axis, a Y-axis and a Z-axis with respect to the workpiece, which comprises: a spindle support structure including a base adapted to be located on a floor surface and having guides extending in the direction along the X-axis on the upper and lower portions thereof, an X-axis slider guided along the guides on the upper and lower portions of the base to move from side to-side in the direction along the X-axis, a Y-axis slider guided to move upwardly and downwardly in the direction along the Y-axis on the X-axis slider, a Z-axis slider guided to move forwardly and backwardly in the direction along the Z-axis on the Y-axis slider, and a spindle head fixedly mounted on the Z-axis slider or mounted to be rotatable in at least one of directions along an A-axis, a B-axis and a C-axis; a workpiece support structure including a base having spindle support means located at the opposing ends thereof along the X-axis and a workpiece mounting table supported by the spindle support means to allow for rotational indexing about the horizontal axis extending in the direction along the X-axis and having at least one workpiece mounting surface; and a chip discharge means located between the spindle support structure and the workpiece support structure for discharging chips produced in the machining area to the outside of the machining area.
According to an embodiment of the aforementioned numerically controlled machine-tool, the base of the spindle support structure may be configured of an extended base having a plurality of base units coupled to each other along the X-axis, the base unit having a predetermined X-axis unit length, and the workpiece support structure may be configured of an extended workpiece support structure having a plurality of workpiece support structure units coupled to each other along the X-axis with the horizontal axes thereof aligned, the workpiece support structure having a predetermined X-axis unit length.
In the aforementioned embodiment, the X-axis slider of the spindle support structure may be driven in the direction along the X-axis by linear motors disposed along the guides on the upper and lower portions of the base, and the linear motor may include a stator and a mover arranged on the base and the X-axis slider, respectively, in opposed relation to each other so that an attraction force of the stator acting on the mover may reduce the load in gravitational direction exerted on the guide of the X-axis slider.
Further, according to the aforementioned embodiment, the base of the spindle support structure may have longitudinal spaces extending in the direction along the X-axis and opening downwardly in the upper and lower portions of the base, respectively, and each of the longitudinal spaces may accommodate therein a guide for guiding and supporting the X-axis slider and an X-axis feed means for moving the X-axis slider in the direction along the X-axis.
In the aforementioned embodiment, preferably, the workpiece mounting table of the workpiece support structure is formed into a shape of a substantially triangle pole having three workpiece mounting surfaces extending in parallel to the horizontal axis in the direction along the X-axis. Preferably, the workpiece support structure is also provided with a pushing means located between the bottom of the workpiece mounting table and the base for imparting an upward pushing force on the workpiece mounting table.
According to a second aspect of the present invention, there is provided a numerically controlled machine tool for machining a workpiece mounted on a workpiece support unit by moving a spindle with a tool mounted thereon in directions along an X-axis, a Y-axis and a Z-axis with respect to the workpiece, which comprises: a spindle support structure including a base adapted to be located on a floor surface and having guides extending in the direction along the X-axis on the upper and lower portions thereof, an X-axis slider guided along the guides on the upper and lower portions of the base to move from side to side in the direction along the X-axis, a Y-axis slider guided to move upwardly and downwardly in the direction along the Y-axis on the X-axis slider, a Z-axis slider guided to move forwardly and backwardly in the direction along the Z-axis on the Y-axis slider, and a spindle head fixedly mounted on the Z-axis slider or mounted to be rotatable in at least one of directions along an A-axis, a B-axis and a C-axis; a workpiece support structure including a base having shaft support means located at the opposing ends thereof along the X-axis, and a workpiece mounting table supported by the shaft support means to allow rotational indexing about a horizontal axis extending in the direction along the X-axis and having at least one pallet mounting means for detachably mounting on the workpiece mounting table a pallet for attaching a workpiece thereon; a pallet changing means including a pallet stocker located adjacent to the workpiece support structure and a pallet carrier for transporting the pallet between the workpiece mounting table and the pallet stocker; and a chip discharge means located between the spindle support structure and the workpiece support structure for discharging chips produced in the machining area to the outside of the machining area.
According to a third aspect of the present. invention, there is provided a numerically controlled machine tool for machining a workpiece mounted on a workpiece support unit by moving a spindle having a tool mounted thereon in directions along an X-axis, a Y-axis and a Z-axis with respect to the workpiece, which comprises: a spindle support structure including a base adapted to be located on a floor surface and having guides extending in the direction along the X-axis on the upper and lower portions thereof, an X-axis slider guided along the guides on the upper and lower portions of the base to move from side to side in the direction along the X-axis, a Y-axis slider guided to move upwardly and downwardly in the direction along the Y-axis on the X-axis slider, a Z-axis slider guided to move forwardly and backwardly in the direction along the Z-axis on the Y-axis slider, and a spindle head fixedly -mounted on the Z-axis slider or mounted to be rotatable in at least one of directions along an A-axis, a B-axis and a C-axis; and a workpiece rest disposed in the front surface of the spindle support structure for fixedly mounting a workpiece thereon, wherein the base of the spindle support structure is provided with longitudinal spaces extending in the direction along the X-axis and opening downwardly in the upper and lower portions of the base, respectively, the guide located in each of the longitudinal spaces for guiding and supporting the X-axis slider, and an X-axis feed means located along the guide in each of the longitudinal spaces for moving the X-axis slider. In the numerically controlled machine tool described above, preferably, the X-axis feed means is configured of a linear motor including a stator, and the X-axis slider is provided with wiper means for removing dust or chips attached to the guide and the stator of the linear motor.
In the spindle support structure, the X-axis slider constituting one of the components of the movable body capable of moving with respect to the stationary base is guided and supported at the upper and lower edge portions thereof so that the force exerted on the X-axis slider (thrust force and support force) is applied to substantially symmetrical points. As a result, unlike a cantilevered X-axis slider, the X-axis slider is not required to be reinforced by a structural member in order to prevent the distal end portion from being bent or deflected due to a generated moment. The structure can thus be reduced in weight and can be moved at high speed. Generally, a machine tool, especially a machine tool for machining a large workpiece has a long stroke along the direction of the X-axis. Therefore the movable body capable of moving at high speed in the direction along the X-axis greatly contributes to a higher machining rate for the machine tool as a whole and a shorter operating time,-thereby making it possible to improve the efficiency of the machining process.
Further, the provision of the workpiece mounting table supported to be allowed for rotational indexing about the horizontal axis extending in the direction along the X-axis allows the workpiece mounting surface to be set in a position where the surface faces upward or preferably in horizontal position, thus facilitating the setup process. The resulting shortened setup time contributes to an improved operating rate for the machine.
When the workpiece mounting table is provided with pallet mounting means, the workpiece mounting table, in combination with the pallet changing means, makes it possible to automate the job of changing the pallet. Thus, the job of changing the pallet with the workpiece mounted thereon can be improved in efficiency, resulting in an improved efficiency of the machining process.
Further, the longitudinal space formed in the base of the spindle support structure and opening downwardly protects the guides, the linear motors or the feeding means such as the ball screw from chips and therefore eliminates the need of the movable cover normally arranged on the X-axis guide. Hence, this is also effective for reducing the loss of the power for X-axis feed and contributes to an increased speed of the X-axis slider in the direction along the X-axis.
When the X-axis slider is driven by a linear motor, the movement in the direction along the X-axis can be increased in speed. By arranging the stator and the mover of the linear motor to reduce the load in the gravitational direction exerted on the guide of the X-axis slider, on the other hand, the friction resistance of the guide is reduced and thus the speed can be further increased. The service life of the guides and the slide element is also longer.
The chip discharge means is intended to reduce the job of removing chips by discharging into a predetermined place the used cutting fluid and the chips that have been produced in the machining area and naturally dropped. Further, the chip discharge means is arranged to separate the spindle support structure and the workpiece support structure from each other. This arrangement facilitates the production and installation of a large machine tool, while at the same time making it possible to make the spindle support structure and the workpiece support structure modular units. The spindle support structure and the workpiece support structure are of course required to be indirectly coupled to each other by concrete or metal members arranged on the floor.
By combining the effects presented by the configuration described above, the numerically controlled machine tool according to the present invention can shorten the setup process time and the machining time, thereby improving the efficiency of the machining process as a whole.